This invention relates to display devices, such as field emission displays, plasma displays, and flat panel cathode ray tubes, and methods for making and using the same. Specifically, the invention relates to improved spacers for such display devices and methods for making and using the same.
Display devices visually present information generated by computers and other electronic devices. One category of display devices is electron emitter apparatus, such as a cold cathode field emission display (FED). A FED uses electrons originating from emitter tips on a base plate to illuminate a cathodoluminescent display screen and generate an image. A gate electrode, located near the emitters, and the base plate are in electrical communication with a voltage source. Electrons are emitted when a sufficient voltage differential is established between the emitters and the gate electrode. The electrons strike a phosphor coating on the display screen which emits photons to form the visual image.
In a FED, spacers separate the base plate and the display screen. Numerous processes have been developed for forming spacers for FED devices. U.S. Pat. Nos. 5,509,840, 5,232,549, 5,205,770, and 4,923,421, and Holloway et al., Production and Control of Vacuum in Field Emission Flat Panel Displays, Solid State Technology, August 1995, pp. 47-54, all incorporated herein by reference, disclose exemplary processes for forming such spacers.
Numerous materials have been used in the spacers, including ceramic, glass, glass-ceramic, ceramic-reinforced glass, devitrified glass, amorphous glass, metal with electrically insulating coating, bulk resistivity metals such as titanium, aluminum, or chromium oxide, silicon dioxide, silicon nitride, polyamide, or a variation of polyimide, such as Kapton. U.S. Pat. Nos. 5,530,582 and 5,658,832, both incorporated herein by reference, disclose that materials in the form of an aerogel or xerogel may be employed as spacers.
Manufacturers have recognized that a good emitter condition is important to effectively operate display devices. If the emitters become contaminated or oxidized by gases in the display device, the work function of the emitter increases and reduces the current emission, thus degrading the performance of the display device. Several articles discuss the impact of such harmful gases on emitter performance. See Schwoebel et al., Field-Emitter-Array Performance Enhancement Using Glow Discharge Processing, 6th International Vacuum Micro Electronics Conference, Jul. 12-15, 1993; Itoh et al., Influence of Various Gases on the Emission of Field Emitter Arrays, Futaba Corporation, (date unknown); and Schwoebel et al., In Situ Enhancement of Field-Emitter Array Performance, 7th International Vacuum Micro Electronics Conference, Jul. 4-7, 1994, p. 378; all incorporated herein by reference.
One method of reducing the amount of harmful gases in a display device has been to use gettering materials. See Giorgi et al., High-Porosity Thick-Film Getters, IEEE Transactions on Electron Devices, Vol. 36, No. 11, November 1989, pp. 2744-2747. Getters absorb gases, both those generated by components and those leaking in from the atmosphere, thereby minimizing harmful gas in the display device. The getter is often placed in peripheral regions of the display device, such as inactive regions outside the active display area between the base plate and display screen. When the getter is positioned outside the active display area, the size of the respective peripheral area must be increased, reducing the effective display area. Moreover, getters merely absorb gases, and are not used to desorb gases.
U.S. Pat. No. 5,684,356 discloses another method of reducing the damaging effects of harmful gases in a display device. This patent describes a FED device with an insulating layer comprising hydrogen silsesquioxane (HSQ). Under specific operating conditions in the display device, HSQ desorbs hydrogen, thus raising the partial pressure of hydrogen with respect to oxygen and keeping deleterious oxide from forming on the emitters.